获取请求模板是否可以与NSFetchedResultController一起使用？

Question

此代码位于我的Entity + CoreDataProperties.swift文件中：

@nonobjc public class func mFetchRequest() -> NSFetchRequest<Entity> {
    return (getContext().persistentStoreCoordinator?.managedObjectModel.fetchRequestTemplate(forName: "MEntityRequest"))! as! NSFetchRequest<Entity>
}

在我的NSFetchedResultsControllerDelegate扩展代码中，我像这样调用这个函数：

var fetchedResultsController: NSFetchedResultsController<Entity> {
    if _fetchedResultsController != nil {
        return _fetchedResultsController!
    }

    let fetchRequest: NSFetchRequest<Entity> = Entity.mFetchRequest()

    // Edit the sort key as appropriate.
    let sortDescriptor = NSSortDescriptor(key: "name", ascending: true)

    fetchRequest.sortDescriptors = [sortDescriptor]

    let aFetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: self.managedObjectContext!, sectionNameKeyPath: nil, cacheName: "Master")
    aFetchedResultsController.delegate = self
    _fetchedResultsController = aFetchedResultsController

    do {
        try _fetchedResultsController!.performFetch()
    } catch let error as NSError{
        print("Unresolved Fetch Error \(error), \(error.userInfo)")
    }

    return _fetchedResultsController!
}

通过在获取请求上设置sortDescriptors，我得到错误：＆＃39; NSInternalInconsistencyException＆＃39;，原因：＆＃39;无法修改不可变模型中的命名提取请求。＆＃39;

当我没有设置sortDescriptors：＆＃39; NSInvalidArgumentException＆＃39;时，原因：＆＃39; NSFetchedResultsController的实例需要带有排序描述符的获取请求＆＃39;

我做得不好？ NSFetchResultsController可以不使用获取请求模板吗？